Ring slicers, also termed ring flakers or stranders, are generally used in manufacturing facilities for manufacturing particle board, oriented strand board, and fiberboard such as MDF. They convert logs, refuse lumber, chips, or other articles of wood into flakes, wafers or strands for the manufactured board products. The ring slicer includes a cylindrical ring assembly for revolution about an axis of rotation. The ring assembly typically includes a large number of elongate knife assemblies, commonly 49 but which may be as many as 72. The knife assemblies support elongate knives having cutting edges extending parallel to the axis of rotation captured between annular end plates. The ring assembly rotates within a chamber into which pieces of wood to be cut or chipped are introduced.
The knives are subject to wear from the wood, and in addition rocks, metal objects and other hard foreign material carried by or with the wood also wear the knives, and may damage or break the knives as well as the knife assemblies. Accordingly, it is routinely required to remove the knives to repair or replace them, or to turn them to expose fresh cutting edges. Moreover, it is episodically required to remove and replace some or all of the knives, the knife assemblies, or both, as a result of “crashes” of the ring slicer apparatus. The machine downtime and the labor required to effect maintenance and repair are costly and desirably kept to a bare minimum.
As described in U.S. Pat. No. 5,313,696, the knives may be mounted to a portable knife assembly that slides radially into slots in the end plates of the ring assembly. Once in place, bolts are inserted through holes in the end plates into threaded holes in the knife assembly to hold the knife assembly in place. In turn, the knife is similarly mounted to the knife assembly with bolts extending through holes in the knife into threaded holes in the knife assembly.
One problem with this approach is that the bolt holes require a tolerance that permits the knife or knife assemblies to move or creep within the ring assembly and thereby to become misaligned or to loosen as a result of the large cutting forces encountered during operation. Moreover, removing the knife from the ring slicer requires both removing the knife assembly from the ring assembly and removing the knife from the knife assembly.
To hold the knife assembly more securely to the ring assembly, the knife assembly may be provided with protruding keys that extend axially into corresponding keyholes in the end plates. The keys and keyholes can be provided with a minimal tolerance of fit that maintains the positional integrity of the knife assembly. However, a major disadvantage of this approach is that the knife assemblies may no longer be simply slid radially away from the ring assembly for maintenance or repair. Rather, the end plates must be axially spaced apart a sufficient amount to permit the projecting keys to clear the end plates, requiring that the entirety of at least one end plate be decoupled from all of the knife assemblies.
It is often necessary to remove a knife from the knife assembly under conditions where it is not otherwise necessary to remove the knife assembly from the ring assembly. U.S. Pat. No. 5,937,923 addresses this problem by providing a clamp for the knife that is biased outwardly by springs disposed in spring holes in the knife assembly, for unclamping the knife without requiring removal of the clamping bolts.
A disadvantage of the mechanism is that it requires the clamp to move radially, and while a necessary indexing of the clamp is provided to seat the clamp into proper position when it is tightened, this is provided in the form of sliding surfaces that wear over time so that the position of the clamp and, therefore, the knife are permitted to wander. Another disadvantage of the mechanism is that it is difficult to remove cut wood fibers introduced into the spring holes when the clamp is loosened. It is yet another disadvantage of the mechanism that the spring forces produced by the multiple compression springs must be well matched to prevent binding of the clamp.
Accordingly, there is a need for a ring slicer having an easily removable knife and knife assembly that provides for positive maintenance of the position of the knife in the ring slicer as well as easy removal of the knife and knife assembly therefrom.